The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
Conventionally, as a refrigerant for use in a vapor compression type refrigeration cycle, Freon series refrigerants were mostly used. In recent years, however, in view of global environmental conservations, as shown in Japanese Unexamined Laid-open Patent Publication No. JP2001-82369 A and Japanese Unexamined Laid-open Patent Publication No. JP2001-99522 A, a refrigeration cycle using a natural refrigerant such as carbon dioxide (CO2) has come to the front.
As a refrigerant system having a CO2 refrigerant refrigeration cycle, for example as shown in FIG. 7, it can be considered that the refrigerant system is provided with a compressor 101, a heat-releasing device (radiator) 102, an intermediate heat exchanger 103, an expansion valve 104, a cooler 105 and an accumulator 106.
The status of the refrigerant in this in-service refrigeration system is illustrated in the Mollier diagram shown in FIG. 8.
As shown in FIGS. 7 and 8, in this refrigeration cycle, the refrigerant is compressed by the compressor 101 to be shifted from the point A to the point B, resulting in a high-temperature and high-pressure gaseous refrigerant. This gaseous refrigerant passes through the heat-releasing device 102 to be cooled by the ambient air to thereby be shifted from the point B to the point C. Subsequently, this refrigerant passes through the intermediate heat exchanger 103 to be sub-cooled by exchanging heat with the return traveling refrigerant, which will be mentioned later, to thereby be shifted from the point C to the point D. Thereafter, the refrigerant is decompressed and expanded by the expansion valve 104 to thereby be shifted to the point D to the point E. Then, this low-temperature and low-pressure refrigerant passes through the cooler 105 to cool the air in a room by absorbing heat from the air. On the other hand, the temperature of the refrigerant itself increases to be shifted from the point E to the point F. Furthermore, the high-temperature and low-pressure refrigerant released from the cooler 105 (i.e., the return traveling refrigerant) is introduced into the accumulator 106 in which only the gaseous refrigerant is extracted. This return traveling refrigerant exchanges heat with the aforementioned forward traveling refrigerant in the intermediate heat exchanger 103 to further increase the temperature to thereby be shifted from the point F to the point A. Then, the refrigerant returns to the compressor 101.
As explained above, in the refrigeration cycle using CO2 as a refrigerant, a supercritical cycle in which the refrigerant pressure exceeds the critical pressure occurs in the high-pressure region in the heat-releasing device 102. Thus, the refrigerant pressure in the high-pressure region becomes higher than that of a refrigeration cycle using Freon series refrigerant, and the refrigerant temperature at the inlet portion of the heat-releasing device becomes higher. Concretely, as shown in the point B in FIG. 8, the refrigerant becomes a high-temperature state exceeding 120° C.
As a result, in cases where an aluminum heat-releasing device with relatively lower heat resistance, which is used in a car air-conditioning refrigeration system, is used as the heat-releasing device 102, there is a possibility that the heat-releasing device components and the like may receive a bad influence by the aforementioned high temperature.
It is an object of the present invention to provide a refrigeration system capable of solving the problems inherent in the aforementioned prior art, keeping the refrigerant temperature lower during the heat-releasing procedure and avoiding harmful effects due to high temperature on a heat-releasing device or the like.
It is another object of the present invention to provide a compressing and heat-releasing apparatus and a heat-releasing device used in the aforementioned refrigeration system.